Freezer evaporator apparatus

ABSTRACT

An ultra low temperature freezer evaporator (ULT) apparatus that has a triple feed capillary tube system. The ULT apparatus prevents the low stage compressor from running in a vacuum. The invention significantly reduces the “pull down” time. Further, the ULT freezer evaporator apparatus significantly increases the transfer area between the evaporator tubing and the contact surface on the unit to assist the transfer of heat from the refrigerated unit through the condenser to the surrounding room.

This application claims benefit of U.S. Provisional Application Ser. No. 61/581,234 filed Dec. 29, 2011, pursuant to 35 USC §119(e).

FIELD OF THE INVENTION

This invention relates to ultra low temperature freezer units, in particular, ultra low temperature (ULT) freezers that have an improved evaporator with an improved capillary feed system on the low stage compressor assembly.

BACKGROUND OF THE INVENTION

Ultra low temperature (ULT) freezers are typically designed to store and protect critical biological materials. Minus 86° C. freezers are a common product produced by several manufacturers. This type of freezer as well as other ULT freezers operating at even colder temperatures is used for the storage of blood component additives, bone marrow, insect cell culture, mammalian cell culture, nucleic acids (DNA/RNA), sperm, fertilized ova, tissues and viruses.

Referring to FIGS. 1 and 2, a typical prior art ULT freezer 80 has one long continuous run of evaporator tubing 20 fed by one extremely long piece (preferably more than 20 feet in length) of capillary tube 22. Such a tube 22 is typically 0.036 inches in diameter. Evaporator tube 20 is typically a ⅜ inch copper tube.

This single length of capillary tube 22 causes the suction pressure of the low stage compressor to run in a substantial vacuum. This vacuum can cause accelerated wear and tear on the crankshaft and connecting rod. In turn, this will drive up the compression ratio of the compressor. Thus, a higher compression ratio can result in the compressor to be running at a pressure exceeding the compressor manufacturer's recommended operating envelope. Of course, operating in such a manner is likely to adversely affect the reliability of the compressor. Further, the flow rate of the refrigerant is reduced in a negative manner. Consequently, longer “pull down” times (the time required for the unit to reach the desired temperature) are experienced. This requires the compressor to run longer as well thus reducing the lifespan of the unit and also increasing operating costs.

As shown in FIG. 3, a lot of transfer area 28, that is, between the contact surface 24 and tube 20, is reduced when evaporator tube 20 is routed around corners 26. Therefore, this design requires a greater amount of time to absorb the heat from inside the unit and transfer this heat from the condenser to the surrounding room. This will also increase the time the compressor must run and increases operating cost.

There is no ULT freezer unit presently available that solves the problems noted above.

SUMMARY OF THE INVENTION

It is an aspect of the invention to provide an ULT freezer evaporator apparatus that has a triple feed capillary tube system.

It is another aspect of the invention to provide an ULT freezer evaporator apparatus that prevents a low stage compressor from running in a vacuum.

Another aspect of the invention is to provide an ULT freezer evaporator apparatus that significantly reduces the “pull down” time.

Finally, it is still another aspect of the invention is to provide an ULT freezer evaporator apparatus that significantly increases the transfer area between the evaporator tubing and the contact surface on the unit to assist the transfer of heat from the refrigerated unit through the condenser to the surrounding room.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric rear view of a prior art freezer illustrating the evaporator tubing configuration in place on the freezer unit.

FIG. 2 is a detailed isometric view of the area of evaporator tubing identified in FIG. 1 as area “B”.

FIG. 3 is a detailed side view of evaporator tubing identified in FIG. 1 as area “C”.

FIG. 4 is a left top isometric view illustrating the evaporator tubing configuration in place on the freezer unit in accordance with the invention.

FIG. 5 is a right bottom isometric view illustrating the evaporator tubing configuration in place on the freezer unit in accordance with the invention.

FIG. 6 is a detailed isometric view of capillary tubes 22A, 22B, and 22C brazed into their respective evaporator tubes 20A, 20B, and 20C indentified in FIG. 4 as area “D”.

FIG. 7 is a detailed isometric view of distributor 32 with capillary tubes 22A, 22B, and 22C leading into raceway 30 identified in FIG. 4 as area “A”.

FIG. 8 is a schematic of the invention used with a preferred ULT freezer evaporator apparatus.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 8 where invention 10 is shown in combination with a typical ULT freezer such as manufactured by Nor-Lake, a Wisconsin Company. This freezer is a two-stage compressor system as shown. This unit is powered by a low noise, high performance cascade refrigeration system using two 1 Horsepower hermetically sealed compressors 40, 50. The high stage compressor 40 is an Emerson Model No. RFT42CIE-PFV for 230-volt units or the RFT42CIE-PFA for the 115-volt unit. The low stage compressor 50 is also made by Emerson using the same model as above.

When the freezer sensor units call for cooling, high stage compressor 40 runs by itself until heat exchanger 42 reaches a temperature of −34 degrees Centigrade. At that time, the controller will start low stage compressor 50 to run with the high stage. The low stage refrigerant will begin to circulate through oil separator 56, downstream to heat exchanger 42 and through filter dryer 60 then to distributor 32 where the refrigerant will be dispersed evenly into three equal length sections 13, 14 and 15 of evaporator invention 10 with each section having capillary tubes 22A, 22B, and 22C inside copper tubing 20A, 20B, and 20C, respectively.

The capillary tubes 22A, 22B, and 22C are of a predetermined diameter and length to cause a predetermined temperature/pressure drop of the refrigerant as it reaches the ⅜ copper tubing 20A, 20B, and 20C that is attached to freezer liner 12. In the example shown in FIG. 8, once the refrigerant is at the evaporator invention 10, the refrigerant will start to absorb heat from the interior of the invention 10 through the freezer liner walls 12.

The three-piece evaporator invention 10 is attached to freezer liner walls 12 with aluminum tape (not shown) to provide better heat transfer. Care must be taken to attach evaporator 10 either level or slightly sloping downhill to aid in refrigerant/oil to return to low stage compressor 50. Refrigerant is fed at the top of the freezer cabinet providing a down feed design, thus letting gravity assist the refrigerant/oil back to compressor 50.

Two sections of evaporator invention 10 are mirror images of each other. FIG. 4 shows evaporator sections 14 and 15. The third section (13) of evaporator invention 10 is shown in FIG. 5 as well as section 14 again. Thus, FIG. 4 shows the back (14), top and left side (15) of the freezer box which corresponds to sections 14 and 15. FIG. 5 shows the bottom, right (13) and again the back (14) of the freezer box which corresponds to sections 13 and 14. Note that the door of the freezer box 80 (in direction 35) is not shown.

The back section 14 is adjusted by reducing the radius of the turns to achieve the same length as the other two sections 13 and 15. The three-evaporator sections tees into a manifold 34, then back to the compressor 50 as shown FIG. 8.

As shown in FIG. 6, capillary tube 22A is brazed into evaporator tube 20A; capillary tube 22B is brazed into evaporator tube 20B; and finally capillary tube 22C is brazed into evaporator tube 20C to form evaporator sections, 13, 14, and 15 respectively.

As shown in FIG. 7, low stage distributor 32 provides refrigerant in direction 36 up raceway 30 where it is split into the three-evaporator sections 13, 14, and 15 as shown in FIGS. 4 and 5.

The use of evaporator invention 10 provides an accelerated “pull down” by providing increased contact area. In fact, when the inventor tested a similar freezer model without evaporator invention 10, it was found that runtime was approximately 40% less to go from ambient temperature to −80 degrees Centigrade.

The high capacity air-cooled condenser 49 features rifled tubing. Having rifled tubing will spin the refrigerant to keep more liquid against the tubing walls for improved heat rejection to the surrounding environment.

Again, referencing FIG. 8, the high stage compressor starts and refrigerant exits compressor 40 through the discharge line to the heat exchanger suction accumulator 44. Part 44 has both low and high temperature refrigerant entering in the dome of the canister. The hot gas makes a couple of passes in ⅜″ tubing inside the canister to boil off any liquid that might be present from the return gas. This heat exchange is to prevent any liquid from entering compressor 40 and causing damage to the bearing surfaces. The refrigerant exits part 44 and travels to condenser 49 where cooler air is drawn across it to lower the temperature of the refrigerant and condense it. Now the liquid refrigerant exits condenser 49 and enters filter drier 48 where particles and moisture are filtered from the refrigerant. The refrigerant enters capillary tube 47 and achieves the right temperature/pressure drop then onward to heat exchanger 42 to absorb heat from the low stage circuit. The refrigerant exits and makes a pass through heat exchanger suction accumulator 44 to boil off any liquid before entering compressor 40 where the refrigerant is drawn into the combustion chamber. Heat of compression will add heat and raise the pressure of the refrigerant where it exits through the discharge line and the cycle will start again.

The low stage compressor 50 will start once heat exchanger temperature reaches −34° c. The refrigerant passes through oil separator 56 where the oil is retained through a coalescing filter and falls to the bottom of oil separator 56. The filtered refrigerant exits and enters heat exchanger 42 where heat is rejected to the high stage circuit. The refrigerant exits and enters filter drier 60 where particles and moisture are filtered from the refrigerant. The refrigerant now enters distributor 32 where the pressure evenly disperses the refrigerant into capillary tubes 22A, 22B and 22C to achieve the right temperature/pressure drop and then onward to evaporator sections 13, 14 and 15. Here the refrigerant will absorb heat from conditioned area 12. The refrigerant enters manifold 34 and returns to low stage compressor 50 where the refrigerant is drawn into the combustion chamber. Heat of compression will add heat and raise the pressure of the refrigerant where it exits through the discharge line and the cycle will start again. Both compressors will run until the cabinet sensor is satisfied.

Although the present invention has been described with reference to certain preferred embodiments thereof, other versions are readily apparent to those of ordinary skill in the preferred embodiments contained herein. 

What is claimed is:
 1. An ultra low temperature freezer evaporator apparatus having a low stage compressor, said apparatus comprising; a triple feed evaporator system having three predetermined equal lengths of capillary tubing within three predetermined equal lengths of evaporator tubing thus providing three evaporator sections, each evaporator section having a compressor end and a raceway end; a freezer cabinet with five freezer liner walls having a top wall, left side wall, right side wall, back side wall, and bottom wall wherein said triple feed evaporator system is attached thereto with one evaporator section attached to the back freezer liner wall, another evaporator section attached to top and left side freezer liner walls, and the third evaporator section attached to the right and bottom side freezer liner walls, wherein said triple feed capillary system prevents the low stage compressor from running in a substantial vacuum and said apparatus having a significantly reduced “pull down” time.
 2. The ultra low temperature freezer evaporator apparatus of claim 1 wherein said evaporator tubing is approximately ⅜ inch copper tubing and the capillary tubing has a diameter of approximately 0.036 inches.
 3. The ultra low temperature freezer evaporator apparatus of claim 1 wherein said triple feed evaporator system is attached to said freezer liner walls using aluminum tape.
 4. The ultra low temperature freezer evaporator apparatus of claim 1 wherein said triple feed evaporator system is attached to said freezer liner walls such that each of said three sections is attached either level or slightly sloping downhill to aid in a refrigerant/oil that is filled from the top of said apparatus to flow downhill thereby facilitating the return of the refrigerant/oil to return to the low stage compressor thus resulting in a down feed design.
 5. The ultra low temperature freezer evaporator apparatus of claim 1 wherein two evaporator sections are mirror images of one another.
 6. The ultra low temperature freezer evaporator apparatus of claim 1 further comprising a manifold wherein each compressor end of said three evaporator sections are connected thereto and wherein said manifold leads back to the low stage compressor.
 7. The ultra low temperature freezer evaporator apparatus of claim 1 further comprising: a raceway wherein each raceway end of said three evaporator sections are connected thereto: a distributor connected to said raceway which delivers refrigerant/oil to said raceway.
 8. The ultra low temperature freezer evaporator apparatus of claim 1 wherein the triple feed capillary system increases the contact area between the freezer liner wall and the evaporator tubing by eliminating the necessity of rounding evaporator tubing around the corners of said freezer liner walls when using a single length of evaporator tubing. 